1. Field of the Invention
This invention relates to a ventilation cap for a fluid passage device, such as a perfusion cannula intended for the passage of blood. More specifically, the present invention relates to a ventilation cap which includes a filter which allows air to be vented out of the device during a flashback-type insertion procedure, while at the same time preventing fluid flow from the device. The present invention further relates to a ventilation cap which is designed to allow simplified detachment and removal of the cap from the device while at the same time minimize incidental blood spillage during removal.
2. Prior Art
Introducer needles, catheters, cannulas and other tubular intravenous devices are commonly used for the passage of body fluids, such as blood, into and out of a patient's body. Such devices often include means such as a flashback chamber for observing the presence of blood during insertion thereof. The "flashback" of blood is an indication of the proper placement of the device in the patient. Devices intended to be placed in fluid flow connection with a vein or artery often employ a transparent flashback chamber into which blood can freely flow when the tip of the device is properly placed within the vein or artery of the patient. The flashback chamber is generally located so as to be in direct fluid communication with the tip of the device intended to be inserted into the body, and to be visually monitored by the medical worker performing the placement procedure. During placement, when the tip of the device accesses a blood flow passage in the body such as a vein or artery, blood will flow through the device into the transparent flashback chamber and become visually apparent to the medical worker, thus indicating proper placement of the tip. Once a device is properly placed in the patient and secured, it is often necessary to connect it to other medical apparatus needed to carry out a desired surgical procedure.
It is very important in the operation of the flashback chamber that means be included therein which permit air to leave the chamber as a result of the entry of blood therein, but which also prevent blood from passing through the vent and exiting the chamber. Due to present concerns about infection by blood-carried diseases such as AIDS and hepatitis, devices which are designed to prevent blood spillage have become highly desirable for use in these types of placement procedures. For example, U.S. Pat. No. 5,032,116 to Peterson et al. discloses a flashback plug which includes a vent membrane of hydrophobic filter material mounted across an internal passage. The plug is adapted to be engaged in airtight communication with a flashback chamber of a cannula insertion device to allow passage of air out of the chamber while preventing the passage of blood. U.S. Pat. No. 5,066,284 to Mersch et al. discloses a ventilation plug adapted to be inserted into a flashback chamber, the plug allows ventilation of air from the flashback chamber through a plurality of air vents drilled by a laser. The air vents are too small to allow passage of blood therethrough. U.S. Pat. No. 4,917,671 to Chang discloses a ventilation plug for a flashback chamber which uses a porous insert to allow ventilation of air and prevent the passage of blood. U.S. Pat. No. 3,859,998 to Thomas et al. discloses a ventilation plug which employs a slitted diaphragm for venting air from the flashback chamber while preventing passage of blood therethrough. U.S. Pat. No. 4,193,399 to Robinson discloses a ventilation plug which is formed entirely of porous plastic material which allows passage of air but prevents the passage of blood.
Although many approaches to ventilation of flashback chambers have been proposed, several drawbacks with the prior art devices still remain. Specifically, the prior art flashback chamber ventilation devices fail to address the problem of accessing the flashback chamber after flashback has occurred without causing a spillage of blood from the chamber in order to connect the device to another medical apparatus, without causing a spillage of blood from the chamber. Prior art flashback ventilation devices are necessarily secured in an airtight manner to the flashback chamber, and are therefore difficult to remove therefrom in order to allow attachment of other medical apparatus. Since the connection between the ventilation plug and the flashback chamber is necessarily extremely tight, it is often difficult to remove the plug without developing substantial vacuum forces within the flashback chamber which cause spillage of blood therefrom when the plug is removed.
Therefore, a need exists in the art to develop a ventilation cap which is designed to avoid spillage of blood from a flashback chamber when removed. There is further a need in the art to develop a ventilation cap in which the seal between the cap and the flashback chamber which hold the cap in airtight connection therewith, can be destroyed prior to removal of the cap from the flashback chamber. These improvements allow a decrease the force necessary to withdraw the cap from the flashback chamber, to prevent the generation of vacuum forces within the flashback chamber during removal and simplify the removal procedure.